Amplifier movements for use with pressure gauges, temperature gauges or the like are well known and have been used commerically for many years. Typically, such gauges have a condition responsive element comprised of a bellows, Bourdon tube, bi-metal coil or the like, providing correlated displacement motion in response to condition changes to which the element is sensitive and exposed. In a common construction, the amplifier or "movement" is comprised of leverage annd gearing operably responsive to displacement motion of the condition responsive element for driving an output shaft supporting a pointer movable relative to a fixed dial plate. The dial registration opposite the pointer position is indicative of the condition state such as pressure or temperature with which the instrument is being operated.
Disclosed in U.S. Pat. No. 4,055,085 to R. H. Wetterhorn is a pressure gauge in which the amplifier movement is supported on the free end of a Bourdon tube for floating conjointly with displacement of the tube end. A remotely connected actuator extending into the motion path of the floating amplifier defines a pivot axis for a hinged segment gear thereof. In pivoting about the actuator axis, the segment gear operably drives a pinion secured on the output shaft supporting the pointer.
Being that such gauge instruments are recognized for their precision of performance, operation accuracy is of paramount importance. Detracting from the intended accuracy, however, is the fact that the gauge movement, which is the heart of the instrument, constitutes a mechanical mechanism comprised of a plurality of geared and linkage components. Each of the individual components are subject to usual industry standards of manufacture that include tolerances which when assembled in operating relation results in a slack or backlash motion adversely affecting ultimate accuracy of the instrument. Traditionally, such instruments have employed a preloaded and subsequently adjusted coiled hair spring to reduce backlash motion in the movement occurring about the connecting linkage. On a low cost gauge, however, the hair spring represents a highly significant cost factor, while in addition can itself contribute adversely to performance accuracy of the gauge. That is, spring rate matching to load is critical in that if the hair spring rate is too low, it is unable to overcome inherent friction of the movement for elimination of the backlash. If too high, the excessive spring load can impose a pre-load friction which likewise detracts from performance accuracy of the gauge. Compounding the foregoing is the fact that spring load inherently varies in the course of winding and unwinding over the normal 270 degree angular displacement incurred by the usual gauge.
Another approach to overcoming the backlash problem of a gauge movement has been an unbalanced weighted construction disclosed, for example, in the Wetterhorn patent supra which relies on the weight of the segment gear, when supported in a vertical orientation, to eliminate all but the tooth-to-tooth clearance between pinion and segment. This approach has been successful in reducing inaccuracy attributed to the movement to within about two percent, but as can be appreciated, is substantially ineffective when the gauge movement is supported horizontally rather than vertically.
Despite recognition of the foregoing, a ready solution affording increased accuracy and/or more universal effectiveness in any support orientation of the instrument has not previously been known.